1. Field of the Invention
The present invention generally relates to an article manufacturing line which includes a series of treating or processing steps or stages (also referred to as the processes) and which incorporates at least one batch process where treating is simultaneously preformed on a plurality of lots collected in a batch (i.e., on a batch-by-batch basis). In particular, the present invention is concerned with an automatic lot organization method and apparatus for carrying out automatic organization and/or reorganization of lots in batches for batch processing or treating. In particular, the invention concerns a semiconductor device manufacturing line which includes an automatic lot organization (or regrouping) apparatus as well as a method of automatically organizing or regrouping lots which are to undergo identical treatment on a batch basis in a succeeding process or processes.
2. Description of the Related Art
For better understanding of the invention, the technical background thereof will be described in some detail by reference to FIG. 11 which is a schematic diagram showing a known semiconductor wafer manufacturing line in which lot organization or regrouping is performed between a lot-based process where semiconductor wafers are treated on a lot-by-lot basis and a batch process where a plurality of lots are simultaneously treated on a batch-by-batch basis. In the figure, reference characters A, B, C and D designate individual lots, wherein lots designated by a same reference character are those which are to undergo treatment on the same conditions in the batch process, while numerals indicate the order or sequence in which the lots A, B, C and D have been transferred to a process where a predetermined number of the semiconductor wafers are to undergo the same treatment, simultaneously.
Now, description will be made of a lot organization method adopted heretofore in a semiconductor wafer manufacturing line. Referring to FIG. 11, the lots A to D arrived at the current process in the order indicated by the numerals 1 to 10 are once stored in predetermined places to wait for lot organization on a batch basis and loading in a treatment process (such as, for example, a pre-treatment for wetting the semiconductor wafer before a diffusion process, such as a thermal diffusion process, an etching process, a photolithography process or the like) with priorities of loading allocated to the semiconductor wafers being altered, as occasions require. Heretofore, this lot storing/regrouping process has been carried out manually by workers, and the lots are classified into groups or sets in accordance with the conditions for the treatments which the lots are to undergo (such as, for example, types of the treatings such as diffusion, etc., temperatures of the treatings, temporal durations or periods required for the treatings, types of gases used in the treatment and others). Thus, the process includes a so-called lot organization process.
Referring again to FIG. 11, it is assumed that tenth and eleventh lots A10 and B11 are transported manually from a preceding process in which treating was individually conducted on the lots (i.e., on a lot-by-lot basis) to the current process where treating is to be simultaneously performed for a predetermined number of lots (i.e., on a batch-by-batch basis). These lots A10 and B11 are stored at relevant locations in a stocker facility where the lots destined for identical treatment under identical conditions have already been stocked. In this manner, the lots are organized into groups or sets each including a predetermined number of lots of the same type. It is assumed in the case of the illustrated example that one set includes four lots. Thereafter, the four lots A organized or grouped into one set and allocated with a higher priority are first treated in the current process to be subsequently transferred to a succeeding process where treatment is performed simultaneously for the four lots or individually for each of the lots. Next, the batch including the four lots B is loaded in the treating of another type and then transferred to the succeeding process, which is then followed by treating of the lots C and so fourth, the treatings being conducted in accordance with the priorities imparted to the lots.
In conjunction with automation of such type lot organization as mentioned above, there is disclosed in a Japanese Unexamined Patent Application No. 112339/1987 (JP-A-62-112339) a lot organization apparatus for organizing semiconductor substrates used in semiconductor device manufacturing processes into groups or sets each housed in a wafer cassette. However, this apparatus is inherently designed for use in a wafer-by-wafer process for trial manufacture or a small-scale manufacture of large varieties of semiconductor substrates.
The hitherto known semiconductor wafer manufacturing scheme illustrated in FIG. 11 in which the lot organization process is manually carried out by relying on the judgement of worker(s) suffers a serious problem that artificial errors can not be avoided incurring, consequently, a false or erroneous lot organization as well as misplacement of the lots in the loading sequence, which results in the unwanted situation in which some lots are left in the stocked state over an extended period without being loaded in the process. Further, the known lot organization scheme can not easily and rapidly cope with modifications or alterations in the number of the conditions for the treatings as well as changes of environmental conditions of the relevant production lines. More specifically, in the case of the known manufacturing process, the optimal conditions for treating have been determined by repeating such trial-and-error procedure that upon occurrence of unsatisfactory product as a result of treating under certain conditions, the latter are then replaced by other conditions. Thus, a large amount of time is required for establishing the optimal conditions for the treatment and hence for the lot organization. Besides, when one of the optimal conditions has to be altered, then the procedure for determining the optimal conditions as a whole has to be repeated from the beginning with the optimal conditions once established previously being discarded. Apparently, the workers will encounter great difficulty in determining the optimal conditions by taking into account the priorities of the treatment which the wafers are to undergo as well as the conditions for the treatment.
The lot organization apparatus disclosed in the publication JP-A-62-112339 cited above is certainly effective so long as a number of lots treated through a series of processes remains constant. However, this known apparatus is not suited for manufacturing a variety of devices by changing throughput such as in the case where the number of lots has to be changed between the preceding and succeeding processes (such as encountered in, for example, the diffusion process in manufacturing the semiconductor device). In other words, the diffusion process (e.g. oxidation process, LPCVD (Low Pressure Chemical Vapor Deposition) process and others) which requires a high relative process ratio (i.e., ratio of the time required for a particular process to a total time taken for the manufacturing) incurs a remarkable time consumption inclusive of the time for rising up the temperature of wafer and cooling thereof (e.g. ten hours or more). Thus, in order to enhance the manufacturing efficiency, it is desirable to treat the semiconductor wafers on a batch basis by collecting or organizing the lots to be subjected to a same treatment in a same set or group. However, in many cases, the number of lots grouped or organized into a set will change in dependence on the types or conditions of treatments, which can not satisfactorily be coped with by the apparatus described in the above-mentioned publication.